An organism maintains its “life” by exchanging much information to each other among the constituent tissues or cells. The exchange of information is mediated by chemical substances such as a neurotransmitter, a hormone, and a cytokine, particularly a large number of peptide factors. Therefore, many endogenous regulatory peptides have been extracted from organisms and subjected to structure determination, and their functions have been clarified. However, almost all these functional peptides have no function only by being translated to proteins from the genes, and hence, there is no way but to search the peptide by purifying the peptide from an organism and evaluating its function. Therefore, a large number of unidentified functional peptides may exist. In addition, if the function is identified once, a search for another role that the peptide may have is not attempted (Non-patent Document 1).
However, because the fact that cytocrome c, which has been known as a protein involved in the mitochondrial electron transport chain for a long time, transfers from the mitochondria to a cytoplasm to induce the apoptosis (programmed cell death) of the cell has been accidentally found recently (Non-patent Document 2), the inventors of the present invention considers that many proteins and peptides other than cytochrome c probably have quite-different multiple biological functions. Further, as described above, many biological regulatory peptides are subjected to various limited proteolysis and converted into matured peptides after being transcribed and translated from the genes, and in this time, many fragment of peptides are produced simultaneously. In general, it is widely considered that these peptides are produced as by-products in order to produce intended biological regulatory peptides and have no function in themselves. However, there is no foundation in the view at all, and for example, actually, the function of glucagon-like peptide 1 which was generated at the same time as glucagon was produced was accidentally identified (Non-patent Document 3). The inventors of the present invention conceive that many peptides generated by cleavage of the proteins are involved in many homeostatic mechanisms and signal transductions of organisms that have yet to be clarified. Actually, the inventors have discovered recently that many endogenous functional peptides generated by cleavage of the protein may be involved in a mechanism of defending the organism (Patent Document 1 and Non-patent Document 1).
The mammalian has complicate, exquisite defense mechanisms called immune system, to thereby prevent entering bacteria and viruses from outside and process foreign substances taken into the organisms (Non-patent Document 4).
The immunoreaction in individuals are classified into a natural immunity in which the immunity can response immediately but recognition of the immunity is ambiguous, and acquired immunity in which the recognition of the immunity is specific (Non-patent Document 4). In the natural immunity system, foreign substances that enter the body are rapidly processed by the involvement of a neutrophil, a macrophage, the complement system, or the like. On the other hand, in the acquired immunity, a lymphocyte plays an important role. That is, when the lymphocyte recognizes a foreign substance once, the substance is memorized by the lymphocyte forever, thereby, when the lymphocyte meets the same substance again even after a long period, the immunity reacts more strongly and treats more rapidly than the case of elimination only by the natural immunity. Thus, the immune system establishes the defense mechanism in which the immunity starts from the natural immunity with less specific recognition and transfers to the acquired immunity with more specific recognition (Non-patent Document 4).
In the natural immunity, there is the neutrophil as a leukocyte that plays an important role at first (Non-patent Documents 4 and 5). As the main function of the neutrophil, a defense reaction to the invasion of foreign substances and microorganisms is mentioned. That is, when a microorganism invades the body, the neutrophil passes the blood vessel wall and infiltrates the bacterial nest to exhibit phagocytosis and disinfection abilities, thereby playing its role (Non-patent Document 5). Thus, the infiltration of the neutrophil to the tissue aims at eliminating the foreign substances and repairing the tissues for the organism. However, if these reactions become excessive, the elimination of the foreign substances leads to the destruction of the tissues, and there may be such a danger as a precipitating factor that the destruction of the tissues leads to the myocardial infarction and the organ dysfunction. From the foregoing, the infiltration of the neutrophil to the tissues is likened to “sword with a double edge” having two aspects (Non-patent Document 5).
As a chemotactic factor causing the infiltration of the neutrophil, there is known a protein factor called chemokine in addition to fMLP, leukotriene B4, completion component C5a, and the like (Non-patent Documents 5 and 6). The name of the chemokine is derived from “chemotaxis cytokine” and is a general name of the protein molecule group having the ability of migrating or activating a leukocyte. These are classified into four kinds of subfamilies, CXC, CC, C, and CX3C according to the positional relationship of the Cys residue preserved in the primary structure of the protein (Non-patent Document 6). Of these, the chemokine in which an amino acid residue is inserted between two Cys residues is the CXC subfamily. The typical CXC subfamily is interleukin 8 (IL-8) and the like and these chemokines mainly target the neutrophil (Non-patent Document 6). However, these chemokines are rarely present in general tissues and known as factors synthesized and produced by transcription and translation of the genes after generation of inflammation. However, because the infiltration of the neutrophil is confirmed several minutes after the tissue injury is generated, the rapid infiltration of the neutrophil may not be probably induced by the chemokine.
Then, the inventors attempted the identification of the factor activating the neutrophil, the presence of the factor being predicted but having yet to be identified, by extracting and purifying the factor from the heart where a large amount of the neutrophil are known to infiltrate at the time of ischemia-reperfusion injury. As a result, two kinds of peptide activation factors, i.e., COSP-1 and fCytb have been identified until the present, but these are peptides derived from the mitochondrial protein (Non-patent Document 7 and Patent Document 1). In addition, the presence of a large number of neutrophil-activating factors derived from the mitochondrial protein other than the COSP-1 and fcytb has been clarified simultaneously. Thus, it has been considered that organisms have novel defense mechanisms involved in these factors (Non-patent Documents 7 and 8 and Patent Document 1). That is, when an accidental damage occurs on cells and the cells are killed, the mitochondria in the cells inflates and mitochondrial proteins are released outside the cells. Then, the mitochondrial proteins released are specifically cleaved by a protease such as trypsin and become activation peptides having functions, such as the COSP-1 and fcytb. There may be a novel defense mechanism which processes substances derived from abnormal cells or dead cells, which become harmful substances, as the result that a large number of activation peptides obtaining functions by the cleavage with the protease induce and activate the neutrophil (FIG. 1). Thus, the presence of a large number of neutrophil-activating factors in the organism is clarified. In order to reveal the defense mechanism involved in these peptides and further clarify the actual situation of the disease such as the ischemia-reperfusion injury involved in the mechanism, it is essential to identify these peptides. However, if these peptides are identified by isolation and purification form organisms as are conventionally done, extremely much labor and time are required.    Patent Document 1: WO 01/066734, Hidehito Mukai, Yoshisuke Nishi, and Eisuke Munekata    Non-patent Document 1: Hidehito Mukai, Peptide News Letter, 41, 1-2, 2001    Non-patent Document 2: Green, D. R., Cell, 121, 671-674, 2005    Non-patent Document 3: Bataille, D., Jarrousse, C., Kervran, A., Depigny, C., and Dubrasquet, M., Peptides, 7, 37-42, 1986    Non-patent Document 4: Ivan Roitt, Jonathan Brostoff, David Male, Immunology illustrated, Nankodo Co., Ltd., 2000    Non-patent Document 5: Shigeki Mizukami, Leukocyte and biological defense, Kodansha Ltd., 1990    Non-patent Document 6: Yoshihiro Matsumoto, Koji Matsushima, Protein, Nucleic Acid, and Enzyme, 45, 979-984, 2000    Non-patent Document 7: Mukai, H., Hokari, Y., Seki, T., Nakano, H., Takao, T., Shimonishi, Y., Nishi, Y., and Munekata, E., Peptides: The Wave of the Future, 2001, 1014-1015, 2001    Non-patent Document 8: Mukai, H., Matsuo, Y., Kamijo, R., and Wakamatsu, K., Peptide Revolution: Genomics, Proteomics & Therapeutics, 2003, 553-555, 2004    Non-patent Document 9: Higashijima, T., Uzu, S., Nakajima, T., and Ross, E. M., The Journal of Biological Chemistry, 263, 6491-6494, 1988    Non-patent Document 10: Higashijima, T., Burnier, J., and Ross. E. M., The Journal of Biological Chemistry, 265, 14176-14186, 1990    Non-patent Document 11: Grant, G. A., Synthetic peptides-A user's guide, 2nd edition, Oxford University Press, 2002.    Non-patent Document 12: Nakajima, T., Wakamatsu, K., and Mukai, H., Methods and Tools in Biosciences and Medicine, Animal Toxins, Rochat, H., and Martin-Eauclaire, M.-F., eds. Birkhaeuser Verlag Basel, Switzerland, pp 116-125, 2000